Optical fiber

Abstract

An optical fiber includes a clad portion and a core portion surrounded by the clad portion. Here, the clad portion is formed by substantially pure quartz, and the core portion has a higher refractive index than the clad portion. The optical fiber is characterized in that a relative refractive index difference of a center of the core portion falls within a range from 0.15% to 0.30%, and a maximum relative refractive index difference of the core portion falls within a range from 0.4% to 0.6%. Here, it is preferable that an average relative refractive index difference of the core portion falls within a range from 0.30% to 0.40%. Here, a mode field diameter of the optical fiber falls within a range from 8.6 μm to 9.5 μm at 1310 nm, and a cable cutoff wavelength of the optical fiber is equal to or lower than 1260 nm. Note that, after the optical fiber is subjected to hydrogen aging, a loss of the optical fiber is preferably equal to or lower than 0.4 dB/km at 1383 nm.

1. An optical fiber comprising a clad portion and a core portion surrounded by the clad portion, the clad portion being formed by substantially pure quartz, the core portion having a higher refractive index than the clad portion,
 wherein a relative refractive index difference of a center of the core portion falls within a range from 0.15% to 0.30% and a maximum relative refractive index difference of the core portion falls within a range from 0.4% to 0.6%, and 
 wherein the optical fiber comprises a refractive index profile such that a refractive index increases one of substantially constantly and substantially monotonically throughout the core portion from the center of the core portion towards an external surface of the optical fiber. 
 
   
   
     2. The optical fiber as set forth in  claim 1 , wherein in the core portion, a part having a high refractive index and a part having a low refractive index are sufficiently distant from each other. 
   
   
     3. The optical fiber as set forth in  claim 1 , wherein an average relative refractive index difference of the core portion falls within a range from 0.30% to 0.40%. 
   
   
     4. The optical fiber as set forth in  claim 1 , wherein a mode field diameter of the optical fiber falls within a range from 8.6 μm to 9.5 μm at 1310 nm, and
 a cable cutoff wavelength of the optical fiber is equal to or lower than 1260 nm. 
 
   
   
     5. The optical fiber as set forth in  claim 1 , wherein a loss of the optical fiber is equal to or lower than 0.4 dB/km at 1383 nm after the optical fiber is subjected to hydrogen aging. 
   
   
     6. The optical fiber set forth in  claim 1 , wherein the refractive index peaks at an external periphery of the core portion. 
   
   
     7. The optical fiber set forth in  claim 6 , wherein the refractive index falls outside of the external periphery of the core portion. 
   
   
     8. The optical fiber set forth in  claim 6 , wherein a refractive index of the clad portion is lower than the refractive index at the external periphery of the core portion. 
   
   
     9. A method of making an optical fiber, comprising:
 forming a core portion surrounded by a clad portion, the clad portion being formed by substantially pure quartz, the core portion having a higher refractive index than the clad portion, 
 wherein a relative refractive index difference of a center of the core portion falls within a range from 0.15% to 0.30% and a maximum relative refractive index difference of the core portion falls within a range from 0.4% to 0.6%, and 
 wherein the optical fiber comprises a refractive index profile such that a refractive index increases one of substantially constantly and substantially monotonically throughout the core portion from the center of the core portion towards an external surface of the optical fiber. 
 
   
   
     10. The method according to  claim 9 , further comprising using vapor phase axial deposition method to form the core portion and the clad portion. 
   
   
     11. The method according to  claim 9 , wherein in the core portion, a part having a high refractive index and a part having a low refractive index are sufficiently distant from each other. 
   
   
     12. The method according to  claim 9 , wherein an average relative refractive index difference of the core portion falls within a range from 0.30% to 0.40%. 
   
   
     13. The method according to  claim 9 , wherein
 a mode field diameter of the optical fiber falls within a range from 8.6 μm to 9.5 μm at 1310 nm, and 
 a cable cutoff wavelength of the optical fiber is equal to or lower than 1260 nm. 
 
   
   
     14. The method according to  claim 9 , wherein a loss of the optical fiber is equal to or lower than 0.4 dB/km at 1383 nm after the optical fiber is subjected to hydrogen aging. 
   
   
     15. The method according to  claim 9 , wherein the refractive index peaks at an external periphery of the core portion. 
   
   
     16. The method according to  claim 15 , wherein the refractive index falls outside of the external periphery of the core portion. 
   
   
     17. The method according to  claim 15 , wherein a refractive index of the clad portion is lower than the refractive index at the external periphery of the core portion.